Bead Size Converter
Seed bead aught to mm.
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About Bead Size Converter
Look up seed bead sizes in the aught ('0') system and their millimetre size, plus how many beads fit per inch. Pick a size and see the round-bead and cylinder (Delica) millimetres side by side.
The aught system is backwards — a bigger number is a smaller bead — and the millimetre size shifts by brand, so a plain chart can mislead; this shows ranges and separates round from cylinder beads. It is completely free with no sign-up, and it runs entirely in your browser.
Frequently asked questions
- What size is an 11/0 seed bead in mm?
- About 1.8–2.2 mm across for a round seed bead, with roughly 18 beads per inch. Japanese 11/0 beads run a touch smaller and more uniform than Czech ones.
- Why is a bigger aught number a smaller bead?
- The number is an old count of how many beads fit in a given length, so more beads means each one is smaller — a 15/0 is smaller than an 8/0. It's read '15-aught'.
- Is a Delica the same size as a round 11/0?
- No. Miyuki Delicas are cylinder beads, so an 11/0 Delica (about 1.6 mm) is a different size and shape from an 11/0 round seed bead, even though they share the aught number.
- Do Czech and Japanese seed beads differ in size?
- Yes — Japanese beads (Miyuki, Toho) are more uniform and usually a little smaller than Czech beads of the same aught, which is why the tool gives a range rather than one exact number.
- How many seed beads are there per inch?
- Roughly 18 for 11/0, 12 for 8/0 and 24 for 15/0 — the tool lists an approximate beads-per-inch for each size to help you estimate quantities.